Area Forecast Discussion
Issued by NWS St. Louis, MO

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FXUS63 KLSX 100948
AFDLSX

Area Forecast Discussion
National Weather Service Saint Louis MO
348 AM CST Wed Jan 10 2018

.SHORT TERM...  (Through Late Tonight)
Issued at 346 AM CST Wed Jan 10 2018

Will continue the dense fog advisory for now, though parts of it may
need to be cancelled early if visibilities do not fall off in the
next few hours.

Visibilities have finally decreased to around 1/4 mile over parts of
southeast Missouri and south central Illinois.  Webcams in the St.
Louis area were beginning to show decreased visibilities in fog
also.  In contrast, observations over central Missouri are higher
but ceilings are quite low.  This is partially because of higher
winds and better mixing over central Missouri.  Plan on keeping the
advisory for now across the entire area and evaluate if parts of the
area need to be cancelled around sunrise when visibilities typically
drop to their lowest.  Otherwise, forecast soundings do show that
there may be some breaks over central Missouri later today.
Otherwise, it should be another mainly cloudy day across the region.
While this will cut back on heating, given that temperatures are
already in the 30s and lower 40s and that there will be warm air
advection today, expect highs to reach the low to mid 50s in most
locations this afternoon.

Forecast soundings are showing deep enough low level moisture for
patchy drizzle to persist most of the day across southeast Missouri
into south central Illinois.  By tonight, there will be an increase
in the chance of rain across southeast Missouri and south central
Illinois as a low level jet develops in increasing moisture
convergence over the area.  There will also be an increasing chance
of rain across central and northeast Missouri as well as west
central Illinois overnight as low level moisture convergence
increases under large scale ascent ahead of an approaching upper
trough.  The steady warm air advection will keep surface
temperatures in the upper 40s to lower 50s tonight.

Britt

.LONG TERM...  (Thursday through Tuesday)
Issued at 346 AM CST Wed Jan 10 2018

A return to wintry precipitation is still expected Thursday through
Friday Night. Models remain in good agreement for first wave of
activity as cold front moves through Thursday afternoon/evening. As
temperatures drop behind the cold front, the rain will change to a
mix of freezing rain, sleet and some snow. Do not expect significant
icing with this wave even though temps will drop below freezing over
a very short amount of time. Because of the warmer wx leading up to
this event, ground temps have moderated a bit and qpf amounts will
be less behind the boundary, so just expect a glazing of ice at this
time. Late Thursday night the precipitation will diminish from
northwest to southeast.

Highs on Thursday will range from the upper 40s to low 60s, with
most areas reaching their high temps early in the day, before
dropping.

Still some uncertainty with secondary wave that will move through
the Ohio Valley Friday/Friday night, but all models have trended
further to the east. So kept low chance pops for areas mainly
south and east of St. Louis metro area. By Friday, precipitation
should be all in the form of snow, though some mixed precipitation
is possible for far eastern portions of forecast area. With low
confidence where the system will track, snowfall amounts will be
on the light side at this time.

Beyond that, expect colder than normal temps to persist through rest
of forecast period. Will see several shortwaves move southeast
through region bringing chances for light snow Sunday afternoon
through Monday morning and again Monday night. Timing and strength
of these systems are difficult to judge this far out, so PoPs will
remain in the chance category.

Byrd
&&

.AVIATION...  (For the 06z TAFs through 06z Wednesday Night)
Issued at 1118 PM CST Tue Jan 9 2018

IFR ceilings will persist overnight into Wednesday morning with
patchy drizzle likely. Visibilities vary across the area leading
to low confidence in how low visibilities will become at the
terminals overnight. Regardless, cigs will remain steady into Wed
morning driving the conditions at each site. Winds will become
breezy out of the south by late Wednesday morning and persist
through the afternoon hours. Ceilings are expected to briefly lift
to VFR by Wednesday afternoon before falling back to MVFR by
Wednesday night.

SPECIFICS FOR KSTL:

IFR ceilings will persist overnight into Wednesday morning with
patchy drizzle likely.Visibilities from neighboring terminals vary
 from one terminal to another and leading to low confidence on
how low visibilities will get at the terminal overnight. Winds
will become gusty out of the south by late Wednesday morning
through Wednesday afternoon. Ceilings will slowly lift to VFR
briefly by Wednesday afternoon then falling to MVFR by Wednesday
evening.

Kelly
&&

.PRELIMINARY POINT TEMPS/POPS...
Saint Louis     57  54  60  19 /  20  30  70  60
Quincy          52  49  53  13 /  10  50  60  30
Columbia        56  51  53  13 /   5  30  60  30
Jefferson City  58  51  55  15 /   5  20  60  40
Salem           55  55  61  24 /  20  50  80  80
Farmington      54  53  60  20 /  20  60  80  80

&&

.LSX WATCHES/WARNINGS/ADVISORIES...
MO...Dense Fog Advisory until 10 AM CST this morning for Audrain MO-
     Boone MO-Callaway MO-Cole MO-Crawford MO-Franklin MO-
     Gasconade MO-Iron MO-Jefferson MO-Knox MO-Lewis MO-Lincoln
     MO-Madison MO-Marion MO-Moniteau MO-Monroe MO-Montgomery MO-
     Osage MO-Pike MO-Ralls MO-Reynolds MO-Saint Charles MO-
     Saint Francois MO-Saint Louis City MO-Saint Louis MO-Sainte
     Genevieve MO-Shelby MO-Warren MO-Washington MO.

IL...Dense Fog Advisory until 10 AM CST this morning for Adams IL-
     Bond IL-Brown IL-Calhoun IL-Clinton IL-Fayette IL-Greene IL-
     Jersey IL-Macoupin IL-Madison IL-Marion IL-Monroe IL-
     Montgomery IL-Pike IL-Randolph IL-Saint Clair IL-Washington
     IL.

&&

$$
WFO LSX



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